Field of the Invention
The present invention relates to a liquid ejection head configured to perform recording by ejecting liquid such as recording liquid from ejection orifices onto a recording medium such as paper or cloth.
Description of the Related Art
For example, as described in Japanese Patent Application Laid-Open No. 2004-122463, a general liquid ejection head includes a recording element substrate having an array of a plurality of ejection orifices and a supply port formed therein for the array of ejection orifices, and a support member including a liquid chamber formed therein. The recording element substrate is mounted onto the support member. Thus, the liquid chamber and the supply port are connected to each other, and a path of liquid is defined from the liquid chamber to the ejection orifices. Into the liquid chamber, the liquid is supplied from a liquid tank being a supply source of the liquid. Further, in recent years, in the liquid ejection head, the number of the ejection orifices arranged in an ejection orifice array is increased to satisfy a need for high-speed recording. Accordingly, there has been a need for design of a flow path capable of supplying the liquid such as recording liquid to the ejection orifice array at a high flow rate.
In the liquid ejection head, under a state in which a meniscus of the liquid such as the recording liquid is formed at each of the ejection orifices, energy is applied to the liquid, thereby ejecting droplets of the liquid forward. In this case, the term “forward” means a direction receding from the liquid ejection head with respect to a surface in which the ejection orifices are formed. Into the ejection orifices, an amount of the liquid equal to a volume of ejected droplets is supplied from the supply port side. At this time, menisci at the ejection orifices are significantly vibrated by vibration of the liquid, with the result that liquid droplets to be ejected at the time of next ejection may not be stable. When the liquid droplets are not stable due to vibration of the menisci, quality of an image formed on a recording medium is significantly degraded when the liquid ejection head is, for example, an inkjet recording head. Particularly in a liquid ejection head in which a large number of ejection orifices are arranged at a high density, a flow rate of the liquid per unit time is high. For example, when ejection of a large amount of liquid is started at one time, at this moment, an inertial force of moving the liquid forward is small in the liquid ejection head. Accordingly, the liquid is not sufficiently refilled into the ejection orifices that are positioned downstream of the liquid chamber and the supply port. Thus, next ejection is started under a state in which the menisci at the ejection orifices are concave. Further, when ejection of the large amount of liquid is stopped at one time, at this moment, the inertial force of moving the liquid forward is large in the liquid ejection head. Accordingly, the liquid in the ejection orifices is pushed out by the inertial force, with the result that the menisci at the ejection orifices are convex. Incidentally, in general, the liquid tank, which is the supply source of the liquid, is structured so as to continuously apply negative pressure to the liquid in order to prevent the liquid from dripping from the ejection orifices of the liquid ejection head. With this structure, the liquid supplied from the liquid tank is subjected to application of a force of returning the liquid to an upstream side. Thus, the liquid in a meniscus convex state at the ejection orifices is likely to retreat and return into the ejection orifices after the meniscus convex state.
As described above, in the liquid ejection head, along with ejection of the liquid, at the start of ejection and after the stop of ejection, there is induced such a phenomenon (so-called meniscus vibration) that the menisci at the ejection orifices are convexed forward or concaved backward. Meniscus vibration is intensified as a flow rate of the liquid to be ejected per unit time becomes higher. When a signal for next ejection is input under a state in which the menisci are convexed forward or a state in which the menisci are concaved backward, a large number of small liquid droplets are splashed in the former state, with the result that recording with splashes is formed on the recording medium. Further, in the latter state, ejection speed and an ejection amount are reduced, with the result that recording with a faint part is formed. In the both states, recording quality is degraded.
As described in Japanese Patent Application Laid-Open No. 2004-122463 and Japanese Patent Application Laid-Open No. 2006-240150, in order to suppress meniscus vibration and to keep satisfactory recording quality, a buffer chamber accumulating air bubbles therein is formed in a liquid chamber, or in a flow path extending from a tank to the liquid chamber. The buffer chamber is formed to buffer and attenuate pressure vibration that causes meniscus vibration. In general, the buffer chamber, which accumulates air bubbles therein, can attenuate even quicker pressure vibration, namely, pressure vibration having a higher frequency component when the buffer chamber is formed at a position closer to ejection orifices from which the liquid is ejected. Further, the buffer chamber having a larger volume can attenuate even pressure vibration having larger amplitude.
As described in Japanese Patent Application Laid-Open No. 2004-122463, when the buffer chamber is formed in a halfway point of a liquid flow path extending from the tank to the liquid chamber, a volume of the buffer chamber can be increased. Thus, the buffer chamber can attenuate and buffer even larger pressure vibration. However, in this case, a position of the buffer chamber is distant from the ejection orifices, with the result that the buffer chamber is less likely to attenuate pressure vibration having short cycles. Meanwhile, as described in Japanese Patent Application Laid-Open No. 2006-240150, when the buffer chamber is formed in the liquid chamber, the buffer chamber is located at a position closer to the ejection orifices. Thus, the buffer chamber can attenuate even pressure vibration having short cycles, but it is difficult to increase the volume of the buffer chamber, with the result that the buffer chamber is less likely to attenuate large pressure vibration. After all, when the buffer chamber is formed, it is not possible to achieve both attenuating and buffering even pressure vibration having short cycles, and attenuating and buffering pressure vibration having large amplitude.
It is an object of the present invention to provide a liquid ejection head capable of reliably attenuating meniscus vibration at ejection orifices, which causes degradation in recording quality, and capable of performing recording at high speed with high quality even when the number of the ejection orifices is increased to satisfy a need for high-speed recording and it is necessary to supply ink at a high flow rate.